1. Technical Field of the Invention
The present invention relates to an assembly line system in which a self-propelled carrier, which carries thereon a main assembly component and a plurality of secondary assembly components, is brought to a halt at an intended assembly work station and after the fitting of the secondary assembly components into the main assembly component the carrier makes an exit from the assembly work station.
2. Description of Related Art
Various assembly line systems for the assembly of workpieces by making utilization of self-propelled carriers have been known in the art.
Japanese Patent Application Pub. No. 62-48432 shows an assembly line system. In this assembly line system, a self-propelled carrier carrying thereon assembly components is brought to a halt at an assembly work station where an assembly worker is placed and after the assembly components are assembled to a unit the carrier resumes travelling.
Japanese Patent Application Pub. No. 5-116044 shows an assembly line system. In this assembly line system, a self-propelled carrier carrying thereon assembly components travels along a guide track of tape arranged on the assembly plant floor and the fitting of the assembly components is carried out at respective assembly work stations on the guide track.
Japanese Patent Application Pub. No. 4-283056 shows an assembly line system. In this assembly line system, there are provided a plurality of assembly work stations. Each of these assembly work stations is assigned a respective level of priority in being supplied with workpieces by a self-propelled carrier. When two or more of the assembly work stations make respective workpiece supply requests at almost the same time, these requests are dealt with in the order of descending priorities, in other words a carrier is dispatched to an assembly work station that is given the highest priority level among the assembly work stations that have issued the requests.
Japanese Patent Application Pub. No. 4-210358 shows an assembly line system. In this assembly line system, the length of time (work processing time) necessary for each assembly work station to complete workpiece processing is estimated and stored. In addition, the length of time (conveyance time) necessary for a carrier, loaded with workpieces, to travel to individual destinations (assembly work stations) is calculated. An assembly work station, the conveyance time of which is equal to or less than its estimated work processing time, is selected, and the carrier is dispatched to the station thus selected.
In each of these assembly line systems, workpieces are conveyed by a self-propelled carrier along an assembly line and the assembly of the workpieces is performed at an assembly work station arranged on the assembly line. These assembly line systems, however, present the problem that the entire assembly line must be changed every time there is made a change in the amount of assembly work or in the type of workpiece. For this reason, it is difficult to assemble, at high efficiency, units one by one from workpieces for FAS (flexible assembling system).
Although there may be variations in assembly rate among assembly workers, the carriers usually travel at a fixed speed. As a result, there is produced the possibility that a slow assembly worker causes trouble to other assembly workers. If, however, the speed of assembly line is adjusted to the slow assembly worker, this may result in making a fast assembly worker idle, leading to poor total assembly efficiency.
Accordingly, it is an object of the present invention to provide an improved assembly line system in which a self-propelled carrier carrying thereon workpieces travels along the assembly line and is brought to a halt at an assembly work station for the putting together of the workpieces. The assembly line system of the present invention makes it possible for assembly workers to effectively assemble workpieces to their own assembly rates, for dealing with FAS products without causing trouble to other assembly workers. Additionally, in accordance with the present invention, assembly line areas can be reduced.